I intend to examine neuroanatomical changes in the rat dentate and CA3 hippocampus after experience in differential environments (complex versus isolated environments). I will examine changes in dendritic branching number and length with the Golgi method and changes in cholinergic axonal input from the septal area with electron microscopy of an acetylcholinesterase stain. I will investigate the effects of age of the experience (at weaning or in adulthood) and gender differences on these neuroanatomical measures. I will also examine gender differences in behavior during the environmental exposure as well as after the experience for correlates to the anatomical measures. A better understanding of plastic changes, particularly at the synaptic level, is necessary if we are to understand how experience organizes the brain and behavior.